Merge branch 'mk/blame-first-parent'

"git blame" learnt to take "--first-parent" and "--reverse" at the
same time when it makes sense.

* mk/blame-first-parent:
blame: allow blame --reverse --first-parent when it makes sense
blame: extract find_single_final
blame: test to describe use of blame --reverse --first-parent

diff --cc builtin/blame.c
index 3b80e8fd75cc0743035642cb82a284271925c865,861a5372b9194b71d3f315c72965fb171d4e3392..83612f5b646f1db7232cf69cf5a2ea6b30a6e833
--- 1/builtin/blame.c
--- 2/builtin/blame.c
+++ b/builtin/blame.c
@@@ -2691,9 -2689,7 +2697,7 @@@ parse_done
                sb.commits.compare = compare_commits_by_commit_date;
        }
        else if (contents_from)
 -              die("--contents and --children do not blend well.");
 +              die("--contents and --reverse do not blend well.");
-       else if (revs.first_parent_only)
-               die("combining --first-parent and --reverse is not supported");
        else {
                final_commit_name = prepare_initial(&sb);
                sb.commits.compare = compare_commits_by_reverse_commit_date;